I've received confirmation from the product team that this list cannot be modified, but that new languages will be added in one of the upcoming releases. Can you share with me the list of needed languages, either here or by message, so I can make sure that what you need is known by the teams?
From the feedback I've got from the product team, answer is: no you cannot change this. I've received the list and passed it on to the product team. They should be able to include all of it in the October or November release.
I'm not sure those lists can be extended. I'll double check with the product team to know why there can be some differences. Can you share one example of the differences you noticed and would like to see?